If $x \bigtriangledown y = x-3y$ and $x \bigtriangleup y = x(y-6)$, find $(-5 \bigtriangledown 0) \bigtriangleup 4$.
First, find $-5 \bigtriangledown 0$ $ -5 \bigtriangledown 0 = -5-(3)(0)$ $ \hphantom{-5 \bigtriangledown 0} = -5$ Now, find $-5 \bigtriangleup 4$ $ -5 \bigtriangleup 4 = -5(4-6)$ $ \hphantom{-5 \bigtriangleup 4} = 10$.